Accident & Failure Investigation

How Can Petrochemical Operators Maintain the Integrity of Their Equipment?

A view of an oil refinery lit up at night

Failure analysis at an oil refinery leads to safer designs and revised industrial standards

A significant explosion occurred at a U.S. petroleum refinery after a heat exchanger ruptured, releasing highly flammable hydrogen and naphtha at a temperature of 500 degrees Fahrenheit. The ensuing fireball fatally injured several employees. To identify the root cause of the failure and define steps to help prevent a recurrence, our client called on Exponent to perform a rigorous multidisciplinary investigation.

The Challenge

Exponent was asked by our client to help determine why their heat exchanger ruptured so catastrophically, releasing the flammables involved in the explosion.

The subsequent fire burned for several hours, causing secondary damage to the failed sections of the heat exchanger and surrounding piping and pressure vessels. Damage due to high temperatures from flame exposure on these structures can include weakening of the metal, changes to the grain structure, corrosion, cracking, and distortion due to unequal heat stress. This greatly complicated Exponent's investigation, as the secondary damage obscured preexisting damage to the heat exchanger, the source of the initial failure. Given the post-fire conditions, certain possible damage mechanisms were much more challenging to diagnose, like high-temperature hydrogen attack (HTHA), which can leave microscopic traces that may only be present in small, localized areas of the equipment.

The equipment's susceptibility to damage mechanisms that occurred under the observed operating conditions was influenced by several variables, including its materials of construction, process fluid composition and flow rates, and pressure and temperature.

Exponent's multidisciplinary Solution

Leveraging expertise in thermal sciences and materials and corrosion engineering, Exponent's multidisciplinary team performed an in-depth origin and cause investigation, metallurgical characterization of the failed heat exchanger, and heat transfer analysis to determine the root cause of the deadly explosion.

Exponent's Impact

With Exponent's assistance, our client determined the root cause of the heat exchanger rupture. Our findings have since supported the refinery in making changes to their equipment that helped prevent recurrences and contributed to safer processes for the petrochemical industry.

To maintain the integrity of equipment in high-temperature hydrogen service, the petrochemical industry had previously utilized the Nelson curve, which predicts the occurrence of HTHA as a function of temperature and hydrogen partial pressure; however, our investigation, as well as investigations by other independent organizations, confirmed that predictions from the Nelson curve were not sufficiently conservative to prevent all HTHA equipment failures.

Exponent's careful damage mechanisms review provided a solid foundation for our client, enabling them to establish a more effective inspection strategy and mechanical integrity program, supporting them in identifying and predicting HTHA damage, and ensuring mechanical integrity. Our team also advised our client on opportunities to create a safer equipment design by using HTHA-resistant cladding materials.